William Byrd (c.1540–1623) was an English composer who wrote in every genre prevalent in his day and displayed proficiency in each musical category he attempted. Whether it was sacred or secular vocal music, his consort writing for viols, or his music for the keyboard, Byrd was a supreme musical architect. His writing reached the height of musical sophistication in England during his lifetime.

In Byrd’s day, virginals, harpsichords and all manner of plucked-string keyboard instruments were widely played throughout England. Organs, both large and small, were also in wide use throughout the country. Byrd held an important position as organist at Lincoln Cathedral, and it is certain he would have played many of his keyboard compositions on the organ. Like his contemporaries, he rarely specified the particular keyboard instrument to be used. The uncomplicated reality of the period was that players simply used what was available to them at the time.

Byrd’s keyboard compositions fall broadly into four categories: fantasias, settings of popular songs, variations, and dance pieces. The middle half of the 16th century saw this first genre evolve from a work for lute or viol consort into a keyboard piece. The developing Tudor fantasia featured continuous imitation, rapid figurations and hitherto unknown displays of virtuosity. Above all, it was keyboard writing which was decisively idiomatic. Byrd’s compositions of this type are sectionalised works and are, more often than not, somewhat formulaic. Customarily beginning in the style of a cantus firmus choral motet with long note values, musical ideas are exposed and heard in various registers of the keyboard. This was typically followed by an answering phrase with shorter note values and a sharply contrasted character. New ideas continue to emerge and the writing becomes increasingly more complex and virtuosic. There is habitually a tripla section and a codetta notable for its brilliant scalic writing.

Thus, the Byrd fantasia is a clever and distinctive amalgam of the ancient motet style, with its overlapping entries, and the emerging features of idiomatic keyboard writing formulas. His unique approach to rhythm, which puts his keyboard music in a class of its own, features cross-rhythms, hemiolas, polyrhythms, frequent changes of meters, outrageous syncopation and even jaunty jig-like episodes.